Bottles and wide-mouthed bottles, which are formed by stretch blow molding of injection molded preform, have a thinly formed body portion with a thickness of about 0.3 mm. Because of it, if a mouth of the bottle is sealed by a cap immediately after the bottle is filled with heated contents, the body portion is pulled inside and deformed resulting from a reduced pressure inside the bottle by cooling.
This deformation tends to appear intensively in the thinnest portion resulting from a difference in a thickness distribution of the bottle body portion, and the appearance of the bottle is extremely impaired. In the bottle and the wide-mouthed bottle having a body portion with a circular shaped horizontal section, in order to solve this problem, the body portion is formed to have a polygonal shaped horizontal section and a body wall portion is formed in panel surfaces which are apt to bend inside. This not only can prevent the partial deformation caused by a reduced pressure, but also can enhance the appearance by bending and deforming the panel surfaces in the body wall portion evenly.
A degree of bending of this panel surface is proportional to an area of the panel surface. In contrast with bottles to store fluids such as drinking water, and juice, however, in wide-mouthed bottles to store contents with viscosity including jam, peanut butter, and honey, the contents are apt to remain in corner portions inside created by the formation of the panel surfaces. As a depth of the corner portions increases, it becomes more difficult to take out the contents with a spoon and the like. In addition, a label will be affixed around the body portion. For a number of reasons including them, an area allowed to form a panel surface is limited, and thereby new means capable of preventing the deformation caused by a reduced pressure in the body portion, which do not use the panel surfaces, are desired.